全文获取类型
收费全文 | 3648篇 |
免费 | 74篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 65篇 |
综合类 | 11篇 |
化学工业 | 756篇 |
金属工艺 | 113篇 |
机械仪表 | 79篇 |
建筑科学 | 74篇 |
矿业工程 | 10篇 |
能源动力 | 66篇 |
轻工业 | 862篇 |
水利工程 | 22篇 |
石油天然气 | 10篇 |
无线电 | 177篇 |
一般工业技术 | 435篇 |
冶金工业 | 511篇 |
原子能技术 | 38篇 |
自动化技术 | 496篇 |
出版年
2021年 | 55篇 |
2020年 | 33篇 |
2019年 | 39篇 |
2018年 | 41篇 |
2017年 | 45篇 |
2016年 | 74篇 |
2015年 | 48篇 |
2014年 | 68篇 |
2013年 | 146篇 |
2012年 | 104篇 |
2011年 | 132篇 |
2010年 | 108篇 |
2009年 | 131篇 |
2008年 | 120篇 |
2007年 | 101篇 |
2006年 | 75篇 |
2005年 | 75篇 |
2004年 | 83篇 |
2003年 | 81篇 |
2002年 | 88篇 |
2001年 | 59篇 |
2000年 | 56篇 |
1999年 | 62篇 |
1998年 | 136篇 |
1997年 | 100篇 |
1996年 | 67篇 |
1995年 | 56篇 |
1994年 | 41篇 |
1993年 | 52篇 |
1992年 | 39篇 |
1991年 | 33篇 |
1990年 | 34篇 |
1989年 | 38篇 |
1987年 | 37篇 |
1985年 | 48篇 |
1984年 | 35篇 |
1983年 | 38篇 |
1979年 | 34篇 |
1978年 | 33篇 |
1977年 | 32篇 |
1974年 | 32篇 |
1920年 | 31篇 |
1917年 | 84篇 |
1916年 | 45篇 |
1915年 | 43篇 |
1914年 | 39篇 |
1913年 | 68篇 |
1912年 | 115篇 |
1911年 | 33篇 |
1910年 | 31篇 |
排序方式: 共有3725条查询结果,搜索用时 122 毫秒
991.
Suggests that the placebo in psychotherapy has retained the negative connotation of an inert "nuisance variable," a label that it originally incurred in the field of medicine. In addition, the transition toward more cognitive models of psychotherapy, particularly A. Bandura's (see record 1977-25933-001) theory of self-efficacy, has led to problems in defining the placebo within psychology. This transition has resulted in an awkward interface between certain preferred cognitive metaphors and the negative connotations of a presumably cognitive placebo construct. Suggestions have been made to dismiss the placebo construct from psychology and to do away with the use of true placebo controls in outcome research. The present analysis maintains that (a) the placebo can be adequately defined within psychology, (b) the negative connotation of the placebo label is largely undeserved, (c) the placebo retains a continuing conceptual and empirical utility for evaluating psychotherapy, and (d) the therapeutic efficacy of current therapies is well established even though they have not generally been shown to be more effective than nonspecific treatment. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
M Ryll KH Hinz U Neumann U L?hren M Südbeck D Steinhagen 《Canadian Metallurgical Quarterly》1997,110(7-8):267-271
Nasosinusal polyposis in the pediatric population is uncommon and its etiology is unclear. In this eleven-year retrospective study, we describe the etiologic features and evaluate the effectiveness of endoscopic sinus surgery in 49 children. Patients were divided into three groups according to whether nasosinusal polyposis was either isolated (n = 14), or associated with either asthma (n = 5) or cystic fibrosis (n = 30). An allergy was present in 10% of patients with isolated polyposis, 80% of patients with polyposis associated with asthma, and 19% of patients with polyposis associated with cystic fibrosis. The indications for surgery were disabling symptoms, specially chronic nasal obstruction, rhinorrhea and mouth breathing, and failure to respond to medical treatment. No surgical complications were encountered. Most patients reported improvement in quality of life with reduction of nasal obstruction in 83% of cases and rhinorrhea in 61%. Minor asymptomatic recurrence (i.e. a few micropolyp localized on the roof of the ethmoid cavity) was observed in 22.7% of the cases in this series, and major recurrence with the same functional symptoms as before surgery in 13.6%. However, recurrences were higher in patients with cystic fibrosis, since minor recurrence with no clinical manifestation was observed in 28.6% of cases and major recurrence in 17.8%. Endoscopic sinus surgery must be decided in collaboration with the pediatric and pulmonary physicians, and must be performed skillfully. With a mean follow-up of 4 years, results in this series are encouraging. 相似文献
993.
994.
TJ Watnick KB Piontek TM Cordal H Weber MA Gandolph F Qian XM Lens HP Neumann GG Germino 《Canadian Metallurgical Quarterly》1997,6(9):1473-1481
The gene for the most common and severe form of autosomal dominant polycystic kidney disease, PKD1, encodes a 14 kb mRNA that is predicted to result in an integral membrane protein of 4302 amino acids. The major challenge faced by researchers attempting to complete mutation analysis of the PKD1 gene has been the presence of several homologous loci also located on chromosome 16. Because the sequence of PKD1 and its homologs is nearly identical in the 5' region of the gene, most traditional approaches to mutation analysis cannot distinguish sequence variants occurring uniquely in PKD1. Therefore, only a small number of mutations have been identified to date and these have all been found in the 3', unique portion of the gene. In order to begin analysis of the duplicated region of PKD1, we have devised a novel strategy that depends on long-range PCR and a single gene-specific primer from the unique region of the gene to amplify a PKD1-specific template that spans exons 23-34. This 10 kb template, amplified from genomic DNA, can be employed for mutation analysis using a wide variety of sequence-based approaches. We have used our long-range PCR strategy to begin screening for sequence variants with heteroduplex analysis, and several affected individuals were discovered to have clusters of base pair substitutions in exons 23 and 25. In two patients, these changes, identified in exon 23, would be predicted to result in multiple amino acid substitutions in a short stretch of the protein. This clustering of base pair substitutions is unusual and suggests that mutation may result from unique structural features of the PKD1 gene. 相似文献
995.
In Arizona v. Fulminante (1991), a U.S. Supreme Court majority stated that confessions are similar to, not fundamentally different from, other types of evidence. To evaluate this claim, three mock juror studies compared the impact of confessions to other common forms of evidence. In Experiment 1, participants read summaries of four criminal trials (murder, rape, assault, theft), each of which contained a confession, an eyewitness identification, character testimony, or none of the above. Significantly, the confessions produced the highest conviction rates. In Experiments 2 and 3, participants read a murder or assault trial containing all three types of evidence and made a series of midtrial judgments. Results indicated that the confession was seen as the most incriminating, followed by the eyewitness and character testimony. Although the comparisons we made are limited in certain respects, our findings suggest that confessions are uniquely potent. 相似文献
996.
Motion transparency occurs when multiple coherent motions are perceived in one spatial location. Imagine, for instance, looking out of the window of a bus on a bright day, where the world outside the window is passing by and movements of passengers inside the bus are reflected in the window. The overlay of both motions at the window leads to motion transparency, which is challenging to process. Noisy and ambiguous motion signals can be reduced using a competition mechanism for all encoded motions in one spatial location. Such a competition, however, leads to the suppression of multiple peak responses that encode different motions, as only the strongest response tends to survive. As a solution, we suggest a local center-surround competition for population-encoded motion directions and speeds. Similar motions are supported, and dissimilar ones are separated, by representing them as multiple activations, which occurs in the case of motion transparency. Psychophysical findings, such as motion attraction and repulsion for motion transparency displays, can be explained by this local competition. Besides this local competition mechanism, we show that feedback signals improve the processing of motion transparency. A discrimination task for transparent versus opaque motion is simulated, where motion transparency is generated by superimposing large field motion patterns of either varying size or varying coherence of motion. The model's perceptual thresholds with and without feedback are calculated. We demonstrate that initially weak peak responses can be enhanced and stabilized through modulatory feedback signals from higher stages of processing. 相似文献
997.
This paper introduces compressed eigenfunctions of the Laplace‐Beltrami operator on 3D manifold surfaces. They constitute a novel functional basis, called the compressed manifold basis, where each function has local support. We derive an algorithm, based on the alternating direction method of multipliers (ADMM), to compute this basis on a given triangulated mesh. We show that compressed manifold modes identify key shape features, yielding an intuitive understanding of the basis for a human observer, where a shape can be processed as a collection of parts. We evaluate compressed manifold modes for potential applications in shape matching and mesh abstraction. Our results show that this basis has distinct advantages over existing alternatives, indicating high potential for a wide range of use‐cases in mesh processing. 相似文献
998.
We reconsider the well-studied Selfish Routing game with affine latency functions. The Price of Anarchy for this class of games takes maximum value 4/3; this maximum is attained already for a simple network of two parallel links, known as Pigou’s network. We improve upon the value 4/3 by means of Coordination Mechanisms. We increase the latency functions of the edges in the network, i.e., if ? e (x) is the latency function of an edge e, we replace it by $\hat{\ell}_{e}(x)$ with $\ell_{e}(x) \le \hat{\ell}_{e}(x)$ for all x. Then an adversary fixes a demand rate as input. The engineered Price of Anarchy of the mechanism is defined as the worst-case ratio of the Nash social cost in the modified network over the optimal social cost in the original network. Formally, if $\hat{C}_{N} (r)$ denotes the cost of the worst Nash flow in the modified network for rate r and C opt (r) denotes the cost of the optimal flow in the original network for the same rate then $$\mathit{ePoA} = \max_{r \ge 0} \frac{\hat{C}_N(r)}{C_{\mathit{opt}}(r)}. $$ We first exhibit a simple coordination mechanism that achieves for any network of parallel links an engineered Price of Anarchy strictly less than 4/3. For the case of two parallel links our basic mechanism gives 5/4=1.25. Then, for the case of two parallel links, we describe an optimal mechanism; its engineered Price of Anarchy lies between 1.191 and 1.192. 相似文献
999.
The X.509 certificate stored in a Lightweight Directory Access Protocol (LDAP) certificate repository requires secure and flexible means to make assertions against its component values such as the identity of its owner, issuer, and the intended usage of the public key contained therein. LDAP has traditionally lacked this ability because its string‐based encodings do not have a standardized way of carrying structural information of complex syntaxes as in X.500. The traditional remedies to this limitation are (1) to provide certificate‐specific matching for a limited set of components and their combinations and (2) to extract and store the certificate components in separate searchable attributes. Neither of these remedies is considered complete, because the former lacks flexibility while the latter heightens complexity in managing the integrity of the certificate repository and doubles storage requirements. Owing to the significant downside of these remedies, we investigate the possibility of an Abstract Syntax Notation One‐based Component Matching alternative. In this paper, we present (1) the design and implementation of the LDAP Component Matching for an OpenLDAP directory server to facilitate its use as the certificate repository in Public Key Infrastructure (PKI), (2) various optimization mechanisms to increase the performance of the Component Matching and their implementation in OpenLDAP, and (3) the detailed performance analysis of the LDAP directory server as a certificate repository in comparison with the traditional certificate‐specific matching and the attribute extraction approaches. We show that Component Matching, if equipped with the optimization techniques proposed in this paper, outperforms the traditional approaches. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
1000.
Today, it is widely recognized that optimization methodologies should account for the stochastic nature of engineering systems and that concepts and methods of life-cycle engineering should be used to obtain a cost-effective design during a specified time horizon. The recent developments in life-cycle engineering of civil and aerospace structures based on system reliability, time-dependent reliability, life-cycle maintenance, life-cycle cost and optimization constitute an important progress. The objective of this study is to present a brief review of the life-cycle reliability-based optimization field with emphasis on civil and aerospace structures. 相似文献